1. Response to Signals in Plants Chapter 39

2. Signal Transduction Pathway 1. Receptors receive a stimulus and activate the secondary messengers 2. Secondary messengers ______ the signal in other proteins 3. Cells respond to the signal 1. _____________ pathway 2. Transcriptional regulation

3. Signal Transduction Pathway 1. Light signal activates __________ receptor which initiates two signal transduction pathways 2. Each transduction pathway activates kinase protein 3. Kinase proteins activate the expression of genes that result in a _______ (de-etiolation) response 1 2 3

4. Plant Hormones Hormone: _____________ produced in one part of an organisms body, which _______ another part of the body where it binds with a specific receptor and initiates a response in target cells or tissues  Auxin (IAA)  Cytokinins  Gibberellins (GA)  Abscisic acid (ABA)  Ethylene  Brassinosteroids  Jasmonates  Strigolactones

5. Hormone: Auxin (IAA) Primary location produced:  Shoot apical meristem  Young leaves Major functions:  Stimulates _____________  Promotes lateral and adventitious root formation  Regulates ______________  Phototropism and gravitropism  Promotes secondary growth

6. Polar Transport of Auxin Auxin is transported from apex to shoot Cell wall is _____  Auxin ion picks up H+  Diffuses across plasma membrane Cytosol is _______  Auxin loses H+  Uses energy to pump out H+ to maintain pH  Leaves cell through carrier proteins

7. Cell Elongation in Response to Auxin 3 Low pH activates __________, which separate microfibrils and polysaccharides

8. Hormone: Cytokinins Primary location produced in plant:  Roots Major functions:  Regulate _________ (cytokinesis) and influence pathway of differentiation  More cytokinins = development of shoot buds  More auxins = more root growth  Control apical dominance = apical bud __________________ of axillary buds  Promote lateral bud growth  Stimulate seed germination  Delays senescence (death or deterioration of plant parts)

9. Apical Dominance

10. Hormone: Gibberellins (GA) Primary location produced in plant:  Apical meristems of roots and buds  Young leaves  Developing seeds Major functions:  Stimulate ____________ and _________  Pollen development and tube growth  Promotes _____________ and germination  Stimulates flowering and fruits (with auxin)

11. Gibberellins Role in Germination 1. After being activated by water, gibberellins are released, which signal the aleurone 2. Aleurone releases _____________, which breakdown endosperm 3. Nutrients provide energy to developing embryo

12. Hormone: Abscisic acid (ABA) Primary location produced in plant:  All plant cells Major functions:  ______ growth  Controls stomata under water stress  Promotes seed dormancy (counteracts gibberellins)  Promotes leaf senescence (programed death)

13. Hormone: Ethylene Primary location produced in plant:  Most plant cells Major functions:  Triple response of seedlings 1. Slow stem elongation 2. Thickening of stem 3. Horizontal growth of stem  Promotes ______  ___________ (detachment)  Senescence

14. Movement in Plants Tropism: a directional growth response toward or away from a stimuli _____________: directional growth in response to light  Caused by concentration of Auxin on shaded side

15. Movement in Plants Gravitropism: directional growth in response to _____  Caused by sedimentation of _______ in plant cells.

16. Movement in Plants  Thigmotropism: directional growth in response to _____

17. Plant Response to Light Blue-light photoreceptors  Initiate phototropism  Opening of ______  Slowing of seed leaf stem (hypocotyl) after seedling breaks ground

18. Phytochromes (receptors that absorb mostly red-light)  De-etiolation (greening)  Seed germination  Triggered by accumulation of red and far-red phytochromes  Red phytochrome (P r )  ______ growth  Far-red phytochrome (P fr )  ________ growth  Shade avoidance  Pr and Pfr ratio dictate growth Plant Response to Light Responses to P fr : Seed germination Inhibition of vertical growth and stimulation of branching Setting internal clocks Control of flowering

19. Daily and Seasonal Plant Responses  Circadian rhythms: around 24-hr cycles that are not directly controlled by a known environmental variable  Photoperiodism: a physiological response to photoperiod (interval an organism is exposed to light in a 24-hr period)  Flowering (short-day vs. long-day)  Critical night length

20. Short-day and Long-day Plants  Short-day plants: require light period ______ than some critical period  Long-day plants: require light period _____ than some critical period

21. Critical Night Length  Some plants require a critical night length (ex. 12-hrs) to flower  Flowering can be turned on or off by activating the red (P r ) and far-red (P fr ) phytocrome receptors

22. Flowering Hormone  Flower inducing hormone (______) can initiate flowering in plants not-triggered by photoperiod

23. Plant Response to Environmental Stresses Drought stress  Reduce transpiration  Close _______  Release of __________  Inhibits growth of young leaves  Change leaf shape  Deeper root growth  Drop leaves Dormant Encilia californica

24. Oxygen deprivation  Formation of aerial root  _____ of root cortex cells to create air tubes  Ethylene Plant Response to Environmental Stresses

25. Salt Stress  Salt glands  Production of compatible solutes  Maintain water potential Plant Response to Environmental Stresses

26. Heat Stress  ________ proteins  Chaperone proteins Plant Response to Environmental Stresses

27. Cold Stress  Alter lipid concentration of membranes  Changes in solute concentration of cytosol  ________ proteins Plant Response to Environmental Stresses

28. Plant Response to Pathogens PAMP triggered immunity  Pathogen-associated molecular patterns (PAMPs) = ________________ specific to certain pathogens  Effectors act to cripple host plants innate immune response  R proteins Hypersensitive response = localized ____ _______ near infection site  Lesions Systemic acquired response = signaling molecules activate defense system in entire plant

29. Plant Response to Pathogens 1. Pathogen effector binds with R protein in host plant cell 2. R protein initiates a signal transduction pathway 3. __________________. Infected area is sealed off, with cell walls reinforced. Anti-microbial molecules are released and infected area dies. 4. Infected cells release signaling molecule 5. Signaling molecule transported throughout plant 6. Signaling molecule initiates signal transduction pathway 7. _____________________. Plant cells produce molecules that protect the cell from pathogens.

30. Plant Response to Herbivores Herbivory: animals eating plants  Recruitment of _____________

31. Plant Response to Herbivores Production of _______________  Tannins  Opium

32. Plant Response to Herbivores  Timing of flowering